Fax service is crucial in any business portfolio and so currently mobile network operators should provide a service to this type of customers with the requirements used in other data services supported by today wireless networks: security, seamless and fast service providing and operation. Nevertheless, commonly 3G network operators around the world don't support fax over their 3G networks and they usually work in conjunction with VoIP (Voice over IP) service providers to supply the fax service to customers. The typical situation is that the operators offer a fax service but this may be using their 2G networks.
Generally, enterprise customers with heavy fax traffic can use a fax server running on a server computer which is equipped with one or more fax-capable modems attached to PSTN by fixed telephone lines or, more recently, using software modem emulators which support T.38 (“Fax over IP”) technology to transmit the signal over an IP network. Its function is to accept documents from users, convert them into faxes, and transmit them, as well as to receive fax calls and either store the incoming documents or pass them on to users. Users may communicate with the server in several ways, through either a local network or the Internet. In a big organization with heavy fax traffic, the computer hosting the fax server may be dedicated to that function, in which case the computer itself may also be known as a fax server.
The typical scenario where T.38 is used is T.38 Fax relay (ITU-T Recommendations), wherein a T.30 fax device sends a fax over PSTN to a T.38 Fax gateway which converts or encapsulates the T.30 protocol into T.38 data stream. This is then sent either to a T.38 enabled end point such as fax machine or fax server or another T.38 Gateway that converts it back to PSTN G.711 or PCM (pulse-code modulation) or analogue signal and terminates the fax on a T.30 device.
At present there are many types of fax transmission techniques depending on the application: analogue faxes of any Group specified to conform the ITU-T Recommendations (T.2 G1 devices and T.30 or T.3 G2 devices), faxes in any of the defined Groups for digital formats (T.30 or T.4 G3 and G4 for T.563, T.503, T.521, T.6, T.62, T.70, T.72, T.411 to T.417), and FAX over IP (T.38). Whatever the supportable version is, the Fax service as such is widely used over the fixed line.
The specifications for (2G and 3G) wireless networks establish voice, data and fax as basic standard services. Today, mobile network operators provide Home routers or Home/Residential Gateways (HG) to ensure continuity between the home local area network (LAN) with the in-home connected devices such as fixed telephones or Faxes and the external world represented by a wide area network (WAN). The WAN connectivity to the fax machine using the HG may be provided through (A)DSL, a cable modem, or a broadband mobile phone technology (2G, 3G or beyond).